Tuesday, December 6, 2011

NuVinci N360 Friction Comparison - I'm Using Something I learned in High School!

The first article I wrote about the NuVinci N360 that explains how it works is here. In the comments on that article, someone mentioned that internal friction was an issue with this type of hub. When I finally finished installing the NuVinci it was a pretty nasty day, and I didn't feel like putting fenders on the bike just to take it on a test ride. Instead, I took a few minutes with a few different types of bikes and compared the spin time of different types of drivetrains. My totally unscientific method was to put each bike in the work stand, shift into the highest gear, give the crank ten revolutions, and time the wheel's spin from when I let go of the crank until it came to a complete stop. I did this 3 times for each bike, and I will post the average spin and longest spin.

NuVinci N360

The first hub was the NuVinci N360 - After ten revolutions, the wheel averaged a spin time of 19.2 seconds, with the longest spin time of 19.8

That is one blurry photo. Schwinn High Sierra, WTB hub.

The second hub was the WTB freehub on my Schwinn High Sierra - that spun for an average of 46.7 seconds. The longest spin for this setup was 48.1 seconds.

Nexus 7

Next I tested a Shimano Nexus 7 speed internal hub. This hub actually had the worst friction of the lot, clocking in an average spin time of 12.3 seconds, with the longest spin at 13.2 seconds.

Like Buttah.

Finally I put my 1973 Raleigh International in the stand. I picked this bike up from a day laborer a few months ago and haven't done a rebuild on the high flange Record hubs yet, so this was going to be a crapshoot. Average spin time on 38 year old Record hubs? 1 minute 11 seconds, with the longest spin clocking in at a whopping 1 minute and 13 seconds.

In conclusion, while there is indeed some friction drag on the NuVinci hub, it is less than the drag on a Nexus, and not too different than a free hub. If you want to ride without drag, find yourself some Record hubs. Otherwise, I don't find the friction drag on the NuVinci to be a real factor; a Nexus has more drag, and the NuVinci is only 20 seconds or so less spin than a regular freehub. I rode that Nexus for a long time and never noticed a difference. If you are racing, that might be a factor, but if you are commuting, I think the benefits of the hub outweigh the drag factor of the NuVinci.

8 comments:

While my own Nexus certainly isn't low drag, I would not have guessed it worse than a much more complex unit. I'm not surprised about the Record. Probably even better are my Campy hubs with the tubular rims. I look forward to hearing of your further adventures.

I think that the way the hub is constructed with balls vs gears makes a difference, though I am no physicist. I know you have a Rohloff hub as well, so if you would like to do an independent test that matches my parameters, it would be cool if you post your results here.

I have the previous model, and I felt like it loosened up after the first few rides, although that may have just been my perception. Still, it might be worth repeating your experiment after a few rides. When I was building mine up, I was very concerned about the drag I seemed to be feeling when I tried to turn the axle. Once it was in a wheel, the drag was less noticeable. Once it was on the bike, I felt like it still didn't spin long enough, but after riding it a while, I felt like it was spinning a lot longer. Of course this spin test represents coasting, and also captures any friction present in the freewheel mechanism. You might get different results with different freewheels.I do have to say that while I am typically one of the slowest riders in any group that I ride with, I seem to coast past everyone on the downhills. Whatever friction that is supposed to be holding me back relative to the traditionally-geared bikes does not seem to working.

There are questions about the overall efficiency of the hub, but having ridden one for a few years now, I have no concerns about that. Whatever inefficiencies may or may not exist, I love using the hub, and the only thing I feel that might be holding me back is how fast I move my legs.

I think all that you are testing here is the efficiency of the ratchets on the freewheel - the efficiency of the gear transmission is not being tested at all. I ride a shimano ultrega 27spd, a nexus 8 and a nuvinci 360N, and I'd rate the efficiency in that very order, although I don't have hard figures. Hard data is available from 2001 at: http://www.ihpva.org/HParchive/PDF/hp52-2001.pdfFig 12 shows that at 150W a 27speed set up is about 93%, a Nexus 7 and Rohloff around 91%.I've heard a fixie is about 98%. Nuvinci refuse to release their test results, which is suspicious in itself, but I imagine it's in the low to mid 80s.

Interesting; I am not an engineer, I'm just a hard drinking blogger with a score to settle...

I didn't think to test my fixed gear.

I appreciate the input - I will assume that my test at least shows some sort of worthwhile comparison, though I don't have charts like the ones you linked to. (And to be honest, they made me a little glassy eyed..)

I believe I read where the internal geared hubs will have higher friction because of all of the parts that are in there. If you were to take the hub apart and count the parts the number is many times an open gear setup. Thus the friction. I do not remember if the lubrication plays into this.

About Me

Justin loves cars, especially the "rare but not desireable" kind. As Factotum at The Phoenix Insurance, his duties range from marketing efforts to management of the company's fleet of classic cars and trucks. In his spare time he looks for cars on Craigslist and dares himself to buy them. In his spare spare time, when he should be sleeping, he carves pipes.